Battery separators are commonly employed as a permeable insulating diaphragm interposed between plates of opposite polarity in a battery so that the electrolyte forms the sole connecting path therebetween. The typical separator in a porous diaphragm with parallel longitudinal ribs on one surface thereof. The ribs are normally adjacent the positive plate and the flat side of the diaphragm is adjacent the negative plate.
One type of separator is the so-called "sintered PVC" separator formed by sintering granular polyvinyl chloride upon a moving belt, the rib pattern being formed prior to sintering by suitable die means. One method of making such a separator is described in U.S. Pat. No. 3,450,571.
A method and apparatus have recently been disclosed in copending application Ser. No. 431,146 filed Jan. 7, 1974, now U.S. Pat. No. 3,892,620, for forming envelopes of thermoplastic sheet material such as a battery separator blank made from sintered polyvinyl chloride. In the device disclosed in said copending patent application, the battery separator blanks are fed along a conveying means past a heating station where the blank is heated along a narrow transverse zone, and into a folding and sealing station where the blank is folded into an envelope and heat sealed. While this device is satisfactory, a less complicated and easier to maintain device has been invented which is the subject matter of the present patent application.